When it is intended to electrically operate a screw driver by a conventional electric or hand drill, a drilling tool or bit should be first dismantled from a chuck of the drill and the screw driver is then clamped on the chuck of the drill housing for screw driving purpose. It is quite inconvenient for such a replacing operation by detachably and replaceably mounting the drilling tool or the screw driver on the drill housing. If two hand tools, namely one for the drill and the other for the screw driver, are simultaneously prepared for their parallel uses, their equipment cost and handling inconvenience may be increased.